Water aspirator vacuum source

The water trap is in turn connected to a source of vacuum, most likely, a water aspirator (Fig. 47). 

Suppose, by luck of the draw, you ve had to prepare and purify 1-octanol (B.P. 195°C). You know if you simply distill 1-octanol, you run the risk of having it decompose, so you set up a vacuum distillation. You hook your setup to a water aspirator and water trap and attach a closed-end stick manometer. You turn the water for the aspirator on full-blast and open the stick manometer. After a few minutes, nothing seems to be happening. You pinch the tubing going to the vacuum distillation setup, (but not to the manometer) closing the setup off from the source of vacuum. Suddenly, the mercury in the manometer starts to drop. You release the tube going to the vacuum distillation setup, and the mercury jumps to the upper limit. You have air leaks in your vacuum distillation setup. 

The vacuum adapter is connected to a vacuum source, either a vacuum pump or a water aspirator. Real live vacuum pumps are expensive and rare and not usually found in the undergraduate organic laboratory. If you can get to use one, that s excellent. See your instructor for the details. The water aspirator is used lots, so read up on it. 

If you re going to pull a vacuum in the sublimator, do it now. If the vacuum source is a water aspirator, put a water trap between the aspirator and the sublimator. Otherwise you may get depressed if, during a sudden pressure drop, water backs up and fills your sublimator. Also, start the vacuum slowly. If not, air, entrained in your solid, comes rushing out and blows the crude product all over the sublimator, like popcorn. 

Steam or water powered aspirators make good vacuum sources and can be used to divert bad smells down the sewer (see above). They can be made as shown to the right. If the inlet pressure is high and the size is large enough, this can make a great fume cupboard evacuator. 

After filtering the mixture of sample and organic solvent, the hose connected from the water aspirator to the flask under the Buchner funnel should first be carefully disconnected before shutting off the water source to prevent possible backflow of tap water into the flask, which would contaminate the sample. Prior to evaporation, the solvent waste reservoir should be empty, clean, and dry. Evaporation should be started slowly at reduced pressure to avoid the boiling over of solvent and samples. If by chance the polyphenolic extract boils over into the waste reservoir, immediately release the applied vacuum and transfer the extract back to the original boiling flask. If this is not satisfactory and contamination is a possibility, extraction should be performed again with a new sample. 

For the flowing clock modification two 250-mL graduated cylinders three-way stopcock in-line stopcock 1 m of 2-mm-bore Pyrex capillary tubing meter stick cormecting tubing water aspirator or other rough-vacuum source 1-L trap assorted clamps and ring stands stopwatch thermostat bath appropriate solutions. 

A modest vacuum source (about 20 - 50mmHg) should be available at each bench and is sufficient for rotary evaporation of most solvents, filtering under vacuum, distillation of relatively volatile oils, and similar tasks. This level of vacuum is sometimes provided by a house vacuum system. Alternatively, a water aspirator or small diaphragm pump can be used. 

A source of vacuum, usually a water pump (water aspirator) which is connected to the receiving flask by thick walled rubber tubing (pressure tubing). Sometimes there will be a trap between the water pump and the receiving flask. 

The 15-mL centrifuge tube and adapter are placed in the flask so that the tip of the centrifuge tube is about 3 to 8 mm above the bottom of the flask (Fig. 13). The flask is clamped with a three-prong clamp. Many substances sublime at atmospheric pressure (see following experiment). For vacuum sublimation, the sidearm of the flask leads to an aspirator or vacuum pump for reduced pressure sublimation. The vacuum source is turned on and the centrifuge tube filled with ice and water. The ice is not added before applying the vacuum so atmospheric moisture will not condense on the tube. 

Sometimes you ll need a vacuum for special work like vacuum distillation and vacuum filtration as with the Buchner funnel. An inexpensive source of vacuum is the water aspirator (Fig, 62). 

Material Vacuum source (water aspirator or vacuum pump), Pyrex test tube with side tube and stopcock, stopper, burner copper wool. 

To make this good quality high strength acid, the following materials are needed concentrated sulfuric acid, sodium nitrate, and dry ice. Also required is a distilling kit with ground glass joints and a vacuum adapter so the product can be distilled under a vacuum. The best vacuum source is an aspirator (cost 10) because the acid fumes, will not harm it, and the water flow will flush them down the drain. 

Let us first see how this rapid filtration problem would be handled using chem lab equipment before looking at ways to improvise for the same effect. To begin with, a source of vacuum would be close at hand on the lab bench, such as an aspirator. A water bed pump would serve the same purpose just as well since a really good vacuum isn t needed. From this vacuum source, a vacuum hose similar to an automotive vacuum hose would be led to the glassware set-up shown below ... 

When the water is removed from solution, turn off the heat on the distillation, and carefully apply a vacuum to remove the remainder of the toluene. Then with the vacuum still on, resume heating the flask, and collect the substituted phenylacetone. Methylenedioxyphenylacetone distills at about 140 °C and 160 °C using a good aspirator with cold water. A poor vacuum source leads to much higher distillation temps and tar formation in the distilling flask. The yield from the reaction is close to 150 ml of phenylacetone. Its color should be clear to a light yellow. The odor of methylenedioxyphenylacetone... 

Water, solvents, and corrosive gases should not be allowed to be drawn into a building vacuum system. When the potential for such a problem exists, a water aspirator with a solvent collection device and a trap with a check valve installed between the water aspirator and the apparatus, to prevent water from being drawn back into the apparatus, should be used as the vacuum source. 

Using the procedure described in Technique 16, Section 16.4, distill the product by vacuum distillation using an apparatus fitted with a Hickman still and a water-cooled condenser (Technique 16, Figure 16.5). Place a small piece of a stainless steel sponge in the lower stem of the Hickman still to prevent bumpover and stir vigorously with a magnetic spin vane. Use an aspirator for the vacuum source and attach a manometer if one is available (Technique 16, Figure 16.10). You may use an aluminum block to heat the dishllation mixture. The aluminum block temperature will be about 130°C (with 20 mm Hg vacuum). If you have less than 0.75 mL, you should combine your product with that of another student. 

The Aspirator The most common source of vacuum (approximately 10-20 mm Hg) in the laboratory is the water aspirator, or "water pump," illustrated in Figure 8.7. This device passes water rapidly past a small hole to which a side arm is attached. The water pulls air in through the side arm. This phenomenon, called the Bernoulli effect, causes a reduced pressure along the side of the rapidly moving water stream and creates a partial vacuum in the side arm. 

The primary difference between the apparatus for simple and vacuum distillations is the attachment of the vacuum adapter to a vacuum source. Rather than being directly connected to the vacuum source, the adapter is normally linked to a heavy-walled sidearm flask. This flask has several functions. For example, if a water aspirator is being used to produce a vacuum, the flask serves as a trap to prevent water from backing up into the apparatus, which may occur if there is a sudden decrease in the water pressure in the aspirator. If it is equipped with a stopcock release valve, the flask also provides a means for connecting the apparatus and the manometer to the source of the vacuum and releasing the vacuum. Further discussion of traps is provided under the topic "Vacuum Filtration" in Section 2.17. 

Another common method for removing solvent is by simple distillation (Sec. 2.13). Discontinue heating when only a small amount of solvent remains, and do not overheat the stillpot, as your product may decompose if heated too strongly. The stillpot should be cooled to room temperature, and the receiving flask containing the distillate should be replaced with an empty round-bottom flask. The apparatus should then be set up for vacuum distillation (Fig. 2.42b) and attached to a vacuum source, such as a water aspirator, for a few minutes to remove the last traces of solvent. 

Hickman Still-Rotary Evaporation Apparatus. A simple microscale rotary evaporator for use in the instructional laboratory consists of a 10-mL round-bottom flask connected to a capped Hickman stOl (side-arm type), which in turn is attached to a water aspirator (with trap) The procedure involves transferring the solution to be concentrated to the preweighed 10-mL flask. The flask is then attached to a Hickman stiH with its top joint sealed with a rubber septum and threaded compression cap. The apparatus is connected by the stiU side arm to the trap-vacuum source with a vacuum hose. lAdth the aspirator on, one shakes the apparatus while warming the flask in the palm of the hand. In this manner, bumping is avoided and evaporation is expedited. The stiU acts as a splash guard. Heat transfer is very effective, and once the flask reaches ambient temperature, the vacuum is released by venting through the trap stopcock. 

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